1. Field of the Invention
This invention relates to a portable circular power saw with optical alignment.
2. Description of the Prior Art
When an operator cuts a work piece with a portable circular power saw, the operator draws a cutting line on the work piece and then cuts the work piece with aligning either side surface of the saw blade (edges) with the cutting line.
FIGS. 11 and 12 show a prior art portable circular power saw. When cutting a work piece 316 with this prior art power saw, the operator aligns an edge of a guide piece 312 with the cutting line 15 on the work piece 316 as shown in FIG. 12. Next, the operator rotates the saw blade 301 and pushes the housing forwardly (in the cutting direction) with keeping this alignment condition.
DE3922849 discloses a prior art power saw with optical alignment, wherein the optical guideline is generated on a work piece by a laser emitter. However, the optical guideline is only generated beyond the edge of the base. In other words, this prior art power saw cannot form the optical guideline near the saw blade. The optical guideline system in the power saw requires initial alignment between the saw blade and the optical guideline because the operator selects either of side surfaces of saw blade to be aligned with the cutting line on the work piece. However, in this prior art power saw, it is difficult to conduct the initial alignment between the saw blade and the optical guideline and impossible to align the cutting line with the optical guideline near the saw blade.
U.S. Pat. No. 5,375,495 discloses a portable circular power saw with optical alignment system capable of aligning the optical guideline with the saw blade and with a cutting line near the cutting point.
FIG. 13 shows a side elevation view of this prior art circular power saw with optical alignment system. The laser emitter 404 is arranged, in the cutting direction, in front of the tangential line H at an intersection G of the circumference of the saw blade 402 and the bottom surface of the base 401. The laser emitter 404 emits laser light beam 405 such that a light path of the laser beam 405 contacts the saw blade 402. Moreover, the laser emitter 404 can shift in the direction parallel to the rotation axis of the saw blade 402 to emit the laser beam 405 to align the optical guideline 411 on the work piece 406 generated by the laser beam 405 with either of the side surface 412a or 412b of the saw blade 402.
FIGS. 14A and 14B show alignment conditions in this prior art power saw.
The operator adjusts the position of the laser emitter 404 in either of condition shown in FIG. 14 or 14B in accordance with that the operator intends to cut the work piece 406 on either side of the saw blade 402.
FIGS. 15A to 15E illustrate sectional views shown in the direction E in FIG. 13. FIG. 15A shows an alignment condition of the laser emitter 404, wherein one side surface 412a of the edge portion 402a of the saw blade 402 is aligned with the optical guideline 411. FIG. 15E shows an opposite alignment condition of the laser emitter 404, wherein the other side surface 412b of the edge portion 402a of the saw blade 402 is aligned with the optical guideline 411. FIGS. 15B to 15D show the intermediate alignment conditions between those in FIG. 15A and FIG. 15E. In these alignment conditions, all guideline images have no shadow image of edges of the saw blade on the work piece 406 because the laser emitter 404 is arranged in front of the tangential line H in the cutting direction CD.
This alignment operation is done with the edge of the work piece 406 contacting the edge portion 402a of the saw blade 402 to obtain either of alignment condition shown in FIG. 16A or FIG. 16E.
In this prior art power saw, because the laser emitter 404 is arranged in front of the tangential line H, in order to align the laser beam 405 with either of side surface 412a or 412b, the operator should visually observe the positional relation between the edge portion 402a and the guideline 411 on the work piece 406 with shifting the laser emitter 404 in the direction of the rotation axis of the saw blade 402.
FIGS. 16 and 17 show a portion of the saw blade 402, wherein FIG. 17 shows a side elevation view of the saw blade 402 shown in the direction F in FIG. 16. In FIGS. 16 and 17, each pair of successive edges on the saw blade have different forms and protrudes in opposite directions, and are alternately arranged around the circumference of the saw blade 402. Thus, the resultant cutting width becomes D that is a distance between the both sides of the edges 412a and 412b. In the above-mentioned alignment condition, the optical guideline 411 can be aligned with one side surface 412a of an edge 402a of the saw blade 402 contacting the edge of the work piece 406. On the other hand, the guideline 411 cannot be aligned with the other side surface 412b of edge 402b at the same rotary position of the saw blade 402 because the edge 402b protrudes in the opposite direction to the edge 402a and the edge 402b cannot contact the edge of the work piece 406 in that condition. This was inconvenient.
Moreover, the operator can easily observe the side sight of the saw blade 402 opposite to the motor because of no obstacle structure. On the other hand, the operator cannot easily observe the other side (the side of housing) of the saw blade 402 because the structure blocks the sight.